During operation of certain aircraft, including helicopters that incorporate articulated rotor systems, phenomena such as ground resonance may occur. Ground resonance can jeopardize the safety and operation of the aircraft, and can cause destruction thereof. In general, such phenomena occurs when the aircraft is on the ground, as rotor blades or wings become shifted out of phase with respect to one another and an imbalance of the rotor system results. As the unbalanced rotor system begins to vibrate at the airframe's resonance frequency, any shock transmitted to the rotor system from contact with the ground can further increase the lead or lag of one or more of the blades, thereby causing the rotor system's center of gravity to be displaced from the center of rotation. These violent oscillations can lead to a catastrophic self-destruction of the helicopter within a matter of seconds.
Rotary damper systems have been developed to minimize this effect by damping the lead lag motion of articulated rotor blades. Damping such motion helps stabilize the rotor blades and prevent an irregular spacing between the blades that leads to oscillation induction. Conventional rotary dampers include hydraulic dampers having rotary bearing seals containing damping fluid used to damp system vibrations.
One problem associated with conventional rotary dampers is inadequate sealing of the damper liquid within the hydraulic chambers. In some instances, the use of bearings in traditional dampers has proven to produce unreliable sealing. Unreliable sealing leads to fluid loss, which creates the need for inspection and maintenance on a frequent and routine basis.
To solve this problem, traditional dampers have incorporated internal elastomer seals to contain the damper liquid, but continue to rely on bearings for overall damping functions. This is also problematic as using more parts per rotary damper has led to higher costs and more complicated designs to produce effective sealing and damping during operation.
A further problem associated with traditional rotary dampers is that during routine inspections, traditional dampers must be entirely removed from the rotary wing system in order to be inspected for sealing damage and replacement. Continued removal of the entire damper during its lifetime can decrease quality and/or lifetime of the parts associated with the damper as parts may become loosened or stripped during removal. In addition, as some features of the rotary damper are not visible from the exterior, some degradation may not be detected.
Accordingly, a need exists for rotary dampers and systems having a high reliability and long service life. A need exists for rotary dampers and systems that maximize the performance capabilities of high elastic stiffness and high damping with minimal variations over the operating temperature range of the helicopter. A need exists for rotary dampers and systems with installation characteristics allowing for efficient inspection of elastomer sections without the need for special inspection equipment or removal of the damper from the rotor assembly.